This paper studies a low phase noise voltage-controlled oscillator that is based on a self-aligned on-chip voltage-tunable spherical dielectric resonator. The proposed resonator has been designed for millimeter-wave applications, provides a high quality factor and is voltage controlled. To prove the concept, the circuit is implemented in a 130-nm SiGe BiCMOS technology. It consists of a two stage amplifier and a microstrip feedback path which couples to the resonator. Measurement results demonstrate a phase noise of -95.9 dBc/Hz at 10 MHz offset from the oscillation frequency at 104.03 GHz and a frequency tuning range of 88 MHz. A maximum output power of -9.9 dBm from 32.5 mW dc power is achieved. Simulations based on measurements of the on-chip spherical dielectric resonator indicate that circuit optimizations will lead to an excellent phase noise of -114.8 dBc/Hz at 10 MHz offset. To the best of the authors' knowledge, this circuit is the first reported silicon-based MMIC voltage-controlled oscillator using an on-chip dielectric resonator at millimeter-wave band.